In the field of printed wiring boards, heretofore, forming a permanent mask resist on a printed wiring board has been carried out. In use of a printed wiring board, the permanent mask resist therein plays a role of preventing the conductor layers from being corroded and a role of securing electric insulation between the conductor layers therein. Recently, the permanent mask resist has come to play an addition role as a solder resist film for preventing solder from adhering to any unnecessary part of the conductor layers in a printed wiring board, also in a step of flip chip bonding or wire bonding for mounting semiconductor elements on a printed wiring board via solder.
Heretofore, in production of printed wiring boards, the permanent mask resist has been produced according to a screen printing method using a thermosetting resin composition or according to a photographic method using a photosensitive resin composition.
For example, in flexible wiring boards using a mounting mode of FC (flip chip) bonding, TAB (tape automated bonding) or COF (chip on film) bonding, a thermosetting resin paste is screen-printed and then thermally cured to form a permanent mask resist, except the area of IC chips, electronic members, LCD (liquid-crystal display) panels and interconnection wiring pattern parts (for example, see PTL 1).
On the other hand, in a semiconductor package substrate for BGA (ball grid array), CSP (chip size package) or the like mounted on electronic components, (1) for flip-chip-mounting of semiconductor elements on a semiconductor package substrate via solder, or (2) for wire-bonding of semiconductor elements to a semiconductor package substrate, or (3) for soldering a semiconductor package substrate to a mother board substrate, the permanent mask resist in the bonding part must be removed, and for forming an image of the permanent mask resist, there is employed a photographic method for image formation that includes coating with a photosensitive resin composition, drying it, then curing it through selective irradiation with an active ray such as UV ray or the like, and thereafter removing the non-irradiated part alone through development to form the intended image. The photographic method is suitable to large-scale mass-production owing to the good operability thereof, and is therefore widely used for image formation with a photographic material in the industrial field of electronic materials (for example, see PTL 2).